Why don't railroads need expansion joints?

The title of this video - which might change since I'm writing this up just a day after it was posted to YouTube - is a bit misleading. The actual question in the title - why don't railroads need expansion joints - is only answered in the last half minute or so of the video and is answered more thoroughly in a Practical Engineering video that I'll post after a jump.

The bulk of the video is spent explaining how railroad welds using thermite work. The video explains the nuances far better than other thermite videos I've posted before, explaining why the rails must be aligned and peaked, why the rails must be preheated (including a nice demonstration of heat treating), how the crystal structure changes as a result of the weld, and eventually why the rails don't need expansion joints.

This is the second of at least three thermite videos from Dr Derek. I thought I'd posted the first video to both blogs, but I can't seem to find it, so it'll likely show up next week.

You Spend More on Rust Than Gasoline (Probably)

Heya, Grady. Always good to see ya.

Today's video isn't really all that special. There isn't much revolutionary here, but it's the first in a series about rust and corrosion that Grady has announced and that I'm looking forward to because his garage demos are consistently outstanding. He does show us some bolts in oxygen-rich salt water with time lapse corrosion rolling along. 

I'm looking forward to what he has coming in later installments.

Why SpaceX Cares About Concrete

Grady is back to school us about those tiny 'sparks' that flew away from the launch pad when SpaceX's rocket launched in November 2020.

Apparently the concrete that SpaceX uses for their launch pad isn't quite the same as the concrete that sits as the walkway outside my classroom window.

Grady explains what concrete is (hydrated crystals) and then tests two types of concrete exposed to three heat environments (room temp, home oven, and propane torch) under compression strength tests.

Not shockingly, the heated concretes broke at way less force.

He then goes on to explain how most of this weakness is caused by our old nemesis: thermal expansion.

What Really Happened at the Hernando de Soto Bridge?

I've driven across the Hernando de Soto bridge. It was in 2019 when the wife and I took a vacation down the Mississippi River to see the various flood control measures. Seriously, that's a vacation that we took. Yes, it was my idea. Why do you ask?

This video is more about civil engineering than it is about material science, but around 6:00 there's a good discussion of fatigue-induced failure and how improper welds can lead to that failure.

As I post this (back in July 2021, I work in advance when I have time in the summer), it looks like the bridge is scheduled to at least partially reopen in August 2021. Hopefully by the time this posts in December, I won't have to update it with bad news.

Oh, and that video at 8:58 was taken at about the time I went across the bridge. And the photo right after that was way before I was on the bridge. Neither of those facts inspires a lot of confidence in our bridge inspections. Sorry, Derek.

My YouTube subscriptions

In case you were wondering which science- or material science-themed YouTube channels I subscribed to, you could probably just skim back through and see which video sources I post from most frequently.

But I thought I could put together a list in case you wanted to subscribe to them, too. So, in no particular order...

• Smarter Every Day - Hands down, my favorite channel on YouTube. Destin Sandlin is an engineer turned YouTuber who covers a whole host of science topics both high brow - How Do We Land on the Moon - to low brow - How Do You Harvest Pecans - and covers them all with a humility, curiosity, and ease of communication that is infectious. Occasionally he gets a little too excited about things (check his collaborations with Mark Robert, for example), but most of the time his tone is spot on, and I learn something from nearly every video that he makes. Most tend to be ten to twenty minutes, but occasionally he post forty-five minute to an hour videos and takes a far deeper dive into a topic - take his nuclear sub series, for example. You could easily turn his videos into a year-long science course. I'd take it. He also has a second channel of slightly less polished videos and lots of behind the scenes footage. Destin also spoke at Skepticon about balancing his faith and his science. It's a great talk. His TED talk isn't bad, either. (equally for both blogs)
  
  
• Real Engineering - Initially this channel from Brian James McManus (yes, he's Irish) focused mostly on the rudiments and basics of engineering and used a lot of white on blueprint paper background animation. He's upped his video quality and started using a whole lot more licensed footage over the years, and he now tackles some pretty deep dives into engineering topics (solar panels, renewably powered ships, tesla's battery challenges, colonizing the moon, digital vs vinyl sound, etc). Videos tend to be in the 15-25 minute range anymore. We almost never see Brian, himself, though there have been a couple of videos where we did. I learn a TON from his videos at this point. Initially, I didn't learn nearly as much. (more for MatSci blog)
  
  
• Practical Engineering - Grady Hillhouse reports from his house in San Antonio and makes civil and mechanical engineering incredibly understandable. Some of the best parts in his videos are his small-scale, homemade demonstration aids to help him explain the video's concepts. He's built tiny rivers to show how weirs function, made rebar-reinforced concrete cylinders to show how they improve concrete's resistance to cracking, crafted complex pipe systems to show water hammer, and much more. His videos stick to the 8-12 minute range, and are great explanations of basic engineering concepts. (more for MatSci blog)
  
  
• Veritasium -  Dr Derek Muller hosts - and probably writes - the veritasium channel videos. He originally did all the work himself, but one of his more recent videos celebrating his tenth anniversary on YouTube talked a bit about his increasing team helping him make videos of higher and higher quality. Muller comes out of Canada by way of Australia and is all over the map as far as topics go. His videos are about optical illusions, origami engineering, calculating the speed of light, close packing with shade balls, and - my absolute favorite video of his - how trees get their mass. He covers chemistry, biology, engineering, physics, and general philosophy of science. (equally for both blogs)

• Steve Mould - Steve's videos are far less focused on any one area of science (or of math). He covers everything from "I calculated absolute zero with vodka" to "Tree tumors are GMOs but not made by humans" to "Self driving cars are dangerously confused by LED lights" to "Does Canadian money really smell like maple syrup?". He's a bit of all over the place, in other words, wandering pretty much anywhere that his curiosity happens to take him. The initial videos were pretty low-budget and short (1-4 minutes long), but the quality of video made a pretty big jump about five years ago. The videos have gotten longer over time, some of them wandering to the fifteen minute range, though he still makes a decent number of videos that are in four or five minutes long or shorter. (equally for both blogs)
  
  
• Mark Rober - Mark's all about building bigger, more theatrical versions of everyday things. He's build a scaled up SuperSoaker, filled a pool with jello, and set up the world's largest elephant toothpaste (or devil's toothpaste). He's also built machines to skip stones better than humanly possible, squirrel obstacle courses, and a liquid sand hot tub. Admittedly, most of his videos could be cut by about 25% of their length by eliminating the over-reaction shots. I think his best videos are the most focused. I particularly recommend the rock skipping video.

Why do Baseball Bats Break?

Oh, hey, Grady. Good to see you.

In this video - about why major league baseball saw a sharp uptick in broken bats (and subsequently an uptick of injuries caused by flying bat shards) in the early and mid-2000's - Grady gets into the differences in ash (the wood used to make almost every pre-2000 bat) and maple (a wood that became popular - not poplar - with ball players in the early 2000's after Barry Bonds used one to break the HR record).

He then goes into the non-isotropic nature of wood and how ash and maple are very different. I guess the lessons learned in making ash bats didn't translate cleanly into making maple bats. It doesn't mean that maple bats are inherently less safe, just that they need to be made - and particularly marked - differently than do ash bats.

Really, changing the material requires changing the production and use strategies for that object?

Who would've guessed it?

What is Prestressed Concrete?

"And, of course, I built a demo to show how this works" ~ Grady, 4:10 into the above video

The most wonderful part of the Practical Engineering series of videos is the models that Grady makes to illustrate his lessons.

Of course, he's clearly got a heck of a shop around his house to be able to make those models.

Why Concrete Needs Reinforcement

It's the jorts (2:39), the New Balance shoes, and the pasty, white legs of one Grady Hillhouse that really endear this video to me.

Yes, Grady's style is a little dry, but he does a marvelous job showing very basic concepts of engineering as they apply to our everyday world and not just talking about the concepts but rather by building and showing small, graspable demonstrations.

In this video, Grady shows...

• how much force it takes to break two 'identical' concrete cylinders - one under tension, one under compression
• concrete beams (fairly thick beams) tested to failure with a four-point break test - a beam with no reinforcement, with 'rebar' reinforcement, and with pre-stressed 'rebar' 

Sand Castle Holds Up A Car! - Mechanically Stabilized Earth

I wouldn't want to build my house on a sand castle foundation, admittedly. In fact, I posted something about the dangers of that before

Reinforced sand, on the other hand, looks like it might be something a little different. Just adding in some fabric - or screening - between layers of packed sand makes for a far stronger product. It's almost like it's a composite.

(It is a composite, by the way, gaining new-found strength from the combination of strengths of the materials comprising the composite.)